Reaction liquids obtained when a specimen and a reagent are allowed to react, for example, have been conventionally analyzed by methods using optical techniques. In the case of analyzing a specimen using such methods, an analyzing device is used that provides a reaction field. In the case of analyzing minute amounts of specimens, analyzing devices are used in which a microchannel is formed for transporting a liquid using capillary phenomenon (see, for example, Patent Document 1).
FIG. 17 shows an example of such a microchannel. The microchannel X shown in the figure includes an inflow opening 91, an analysis chamber 92, a discharge opening 93 and an open chamber 94, and is configured to allow a specimen S such as blood to be transported by capillary phenomenon. The analysis chamber 92 has a circular cross-section, and optically analyzes the concentration of a specific component in the specimen, for example, by allowing light to pass therethrough when filled with the specimen. The analysis chamber 92 is defined by a pair of mutually opposing side surfaces 92a and 92b, and a pair of surfaces (not shown) that are perpendicular to the side surfaces 92a and 92b and mutually opposed with a slight distance there between. The open chamber 94 is connected to the analysis chamber 92 via the discharge opening 93. The open chamber 94 is open to the atmosphere by a pathway not shown.
Liquid is transported through the microchannel X in the following manner. First, a specimen S such as blood is introduced into the upstream side of the microchannel X. This specimen S is introduced by capillary phenomenon, and flows into the analysis chamber 92 from the inflow opening 91 as shown in FIG. 18. The vicinities of the side surfaces 92a and 92b constitute regions that are surrounded on three sides by the pair of surfaces and the side surface 92a or the pair of surfaces and the side surface 92b, and facilitate the action of capillary force on the specimen S to increase thrust. Consequently, the specimen S tends to proceed along the side surfaces 92a and 92b. 
However, it is difficult to make the side surfaces 92a and 92b to be completely identical. For example, microscopic variations in shape attributable to the degree of processing accuracy during manufacturing cannot be avoided at the boundaries between the side surfaces 92a and 92b and the pair of surfaces. Alternatively, capillary force varies considerably if oil and the like adhere to the side surfaces 92a and 92b. In such circumstances, a considerable difference occurs between the speed at which the specimen S proceeds along the side surface 92a and the speed at which the specimen S proceeds along the side surface 92b. If this happens, the specimen S unevenly proceeds along the side surface 92a, for example, as shown in FIG. 19. As a result, the specimen S reaches the discharge opening 93 by passing over only the side surface 92a as shown in FIG. 20, thereby causing the discharge opening 93 to be blocked by the specimen S. As a result, an air bubble B1 ends up forming in the vicinity of the side surface 92b. Once this happens, even if analysis is carried out by an optical technique, light radiated onto the analysis chamber 92 ends up passing through the air bubble B1 in addition to the specimen S. Thus, it becomes no longer possible to properly analyze a specific component of the specimen S.    Patent Document 1: JP-A-2004-150804